It is not easy to enter alphanumeric data into a distant computer by telephone. This invention relates generally to a new way of entering alphanumeric data over a communications channel where the terminal equipment has far fewer keys than the number of distinct alphanumeric characters to be conveyed, and relates specifically to a new way of entering character data with no more keys than are found on a touch-tone keypad.
Where alphanumeric data are to be communicated over a telephone line, a traditional approach is to convert the alphanumeric data into a serial binary data stream, and to use the stream to modulate an audio signal which is demodulated at the receiving end. If the data communication is to be two-way, each end of the line must be equipped with a modem (modulator-demodulator). Modems today represent the most commonly used method of character communication over telephone lines. Typically at one end of the line is a human user, and at the other end is a computer.
While modem communications can be very fast and reliable, there is the severe drawback that it requires the human user to have a modem and a terminal or computer. While each telephone instrument represents a potential point of communication, the installed base of such equipped users is far smaller than the number of telephone instruments.
A number of investigators have attempted to exploit the highly standardized touch-tone keypad as a means of entry of information to computers. Where the information to be entered is numerical or composed of prearranged yes/no answers, considerable use has been made of touch-tone keypads. It is well known, for example, for a bank to set up a system permitting account holders to obtain account balances by entering the account number after calling a specially programmed bank computer on the telephone.
Matters become much more difficult if the data to be entered is composed of arbitrary letters of the alphabet, since there are only twelve keys on a touch-tone keypad, and twenty-six possible letters. The well-known mapping of letters to numbers (ABC to the digit 2, DEF to the digit 3, and so on) permits one way for a user to enter letters. But the three-to-one grouping leaves substantial ambiguity when the digits are received. If the received digits are 2, 2, and 8, the letters entered may have been the word BAT or the word CAT, for example. It is well known that Q and Z do not appear on most keypads. Some systems using a keypad for letter input will assign Q and Z to the "1" or "0" digits. Other systems assign Q to the "7" key (along with P, R, and S) and Z to the "9" key (along with W, X, and Y).
One known method for entering alphabetic information via a touch-tone keypad is to use left, right, and center keys, being three additional keys beyond the existing numeric keys, to modify the numeric keys. Left-2, meaning the left key followed by the 2 key, would represent the leftmost of the letters on the 2 key, namely the letter A. Right-2 would represent the letter C, and so on. This has the obvious drawback of requiring twice as many keystrokes as there are letters in the word.
Another approach for communicating characters by a touch-tone keypad is for the user to simply "spell" a desired word character by character until the point that enough digits have been entered that the word is known with certainty. For example, some voice-mail systems allow a caller to enter the name of a desired recipient letter by letter until the recipient is unambiguously determined. This approach is workable, however, only if the universe of possible matches is quite small.
Investigators have also attempted to provide alphabetic information via conventional telephones through speech recognition. A computer receives a speech signal (presumably a word) and attempts to determine which word was spoken. If the recognition was successful, the identified word may be thought of as alphabetic information entered over the telephone line. Speech recognition is fraught with problems, however, since present-day technology does a poor job of getting the right answers. If there is an artificially constrained universe of possible words, the success rate of a speech recognition system can be quite high, but the user may be frustrated with the small permitted vocabulary. Another way to improve the success rate is to demand only that the system manage to recognize the words spoken by a single speaker; this has the drawback that the system cannot accommodate speakers other than the prearranged single speaker.
There is a great need, then, for a simple, reliable way to enter alphabetic information via a telephone line, without the need for a modem or other equipment in addition to the conventional telephone instrument, and without the poor success rate of speech recognition.